21121013891 has 2 divisors, whose sum is σ = 21121013892. Its totient is φ = 21121013890.

The previous prime is 21121013863. The next prime is 21121014017. The reversal of 21121013891 is 19831012112.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21121013891 - 2²⁶ = 21053905027 is a prime.

It is not a weakly prime, because it can be changed into another prime (21121013791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10560506945 + 10560506946.

It is an arithmetic number, because the mean of its divisors is an integer number (10560506946).

Almost surely, 2^21121013891 is an apocalyptic number.

21121013891 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121013891 is an equidigital number, since it uses as much as digits as its factorization.

21121013891 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 864, while the sum is 29.

The spelling of 21121013891 in words is "twenty-one billion, one hundred twenty-one million, thirteen thousand, eight hundred ninety-one".